This invention relates to liquid fuel supply systems in general, and more particularly pertains to fuel/air mixing and modulating systems wherein butterfly type throttle blades cooperate with a throttle body at partial throttle openings to modulate the flow of fuel and air through an air inlet passageway.
It is well known in the art of liquid fuel supply to internal combustion engines that engine efficiency improves as more of the fuel is vaporized or atomized into smaller droplets and evenly homogenized into the fuel/air mixture. The present most commonly employed system for supplying fuel to an engine is with a carburetor which uses a butterfly type valve to regulate the fuel/air supply to the engine. The blades of the valve are typically thin and flat across their entire length, and configured to cooperate with the straight walls of the air intake passageway in which the throttle valve is located. This configuration results in fuel/air mixture flow characteristics around and downstream from the throttle blade or blades which effect the fuel/air mixture adversely with respect to vaporization or atomizing fuel into small droplets and evenly mixing it with the intake air.
In the conventional carburetor using butterfly throttle blades, partial throttle intake mixture flows essentially equally around both sides of the throttle blade. In this configuration, some liquid fuel tends to separate out of the mixture onto the intake passageway walls and throttle blades as the fuel/air mixture passes around the blade edges of the partially closed throttle. No provision is made for the separated fuel to re-enter the intake air for the formation of a homogenous fuel/air mixture. The separated fuel runs along the throttle blade and the walls of the engine intake passageways, and subsequently enters the cylinders in droplets that are too large for efficient combustion, resulting in reduced engine efficiency.
More recent designs have concentrated on the formation of high velocity airstreams through a convergent-divergent portion of the main intake passageway, usually constricted by a movable conical section which functions both as a throttle and a venturi forming device. These designs, when properly engineered, have excellent fuel atomizing and mixing characteristics. However, they have notorious difficulties with proper fuel metering for all engine operating conditions. Additionally, they are difficult and expensive to construct due to the general requirement for a large number of precision machined parts which cannot be constructed using existing carburetor manufacturing tooling and techniques.
The present invention discloses a carburetor throttle and throttle body assembly which can take advantage of fuel separation to achieve better fuel vaporization and atomization, but which avoids the unfavorable fuel separation problems of more conventional designs, yet achieves the partial throttle efficiency of the conical venturi designs without the adverse effects on fuel metering and without the extraordinary and expensive construction requirements.
According to the present invention there is provided a novel carburetor throttle assembly wherein butterfly type throttle blades have regions of cooperation with the throttle body such that channels are formed at partial throttle openings. As the throttle blades rotate open at partial throttle settings, the channels open much more quickly than other seal areas, so substantially all of the part throttle intake mixture flows through the channels. Due to the angles of the channels with respect to the main intake flow path, and due to the high velocity change effected by the channels, separation of liquid fuel onto the throttle body can be controlled or enhanced. The walls of the throttle body can be heated to enhance vaporization of the separated fuel. As convergent high speed fuel/air streams exiting the channels collide downstream from the throttles, liquid fuel is finely atomized and thoroughly mixed with the intake air.
The resulting improvement of fuel atomization and vaporization at partial throttle openings results in a corresponding improvement in engine efficiency at partial load conditions.